Sound recording



Oct. 19, 1937. B. F. MILLER SOUND RECORDING Filed July 5, 1955 Imi FIC-L1.

INVENTOR. @w27-0N FM/L/ EQ BY d/ Y ATTO/eg r and thus produce the ground tone or noise.

Patented Oct. 19, 1937 UNITED STATES PATENT OFFICE United Research Corporation,

Long Island City, N. Y., a corporation of Delaware Application July 5, 1935, Serial No. 29,930

8 Claims.

My invention relates to sound recording and more particularly to sound recording systems and apparatuses employing means to reduce ground noise. f

In my co-pending application #1, Ser. No. 28,109, led June 24, 1935, I have disclosed and claimed an invention in which an anti-ground noise type of variable area sound track was produced by a single speech carrying conductor moving across a light aperture to change the length of the exposed portions of the aperture in accordance with the amplitude and frequency of the sound. Ground noise reduction was obtained by biasing a suflicient amount of current through the conductor so as to 'keep the eX- posed portion of the sound track as small as possible. While the above application contains claims generic to the arrangement disclosed in detail herein, that case specically discloses the use of a triangular aperture in the path of the recording beam, the single conductor moving parallel to the base of the triangular aperture.

Also in my co-pending application #3, Ser. No. 29,931, iiled July 5, 1935, I have disclosed and claimed an invention in which an anti-ground noise type of variable area sound track was produced by a speech current carrying conductor moving across a rectilinear slit in accordance with sound waves. Ground noise reduction was obtained by biasing a suicient amount of current through the conductor so as to hold the zero line of modulation of the conductor as close to the exposed edge or the slit as possible. Although that case also contains claims generic to the herein described arrangements it specifically discloses a single con-ductor for both recording sound and obtaining noise reduction.

In my present invention I disclose a similar type of light valve employing a new and different type of noise reduction. As is well known, ground noise is produced largely by dust, oil, and dirt adhering to the clear portion of the sound track. These particles modulate the light received by the photo-cell of the sound reproducing system 'Ihe texture of the lm and the grain of the emulsion also contribute to the generation of ground noise.

Although ground noise is of practically the same intensity throughout the length of the film, it is naturally much more noticeable during periods when sounds of a low level or no sound at al1 is reproduced.

Due tothe shrinkage of the iilm or inaccuracies r in the reproducing machine, the ,film has a tendency to weave sideways as it passes the sound translating point. This weave is at times suicient to allow one end of the light slit to cut off some of the sound track and thus clip the ends of the wave peaks. Although the peaks of the high level sounds may be cut a substantial amount without any apparent distortion of the reproduced sound, this is not true of. the 10W level peaks.

l It is therefore one object of my invention to 10 keep the center of modulation of the speech current carrying conductor always at the center or the sound track.

Another object is to reduce the amount of clear portion without biasing the speech current carrying conductor.

This is accomplished by providing two vibratory conductors, one carrying the speech currents and the other carrying the biasing current which is regulated in accordance with the envelope of the sound Waves being recorded. A'I'he speech current carrying conductor is adjusted so that its center of modulation is approximately in the center of the sound track. By keeping the center of modulation always in the center of the sound track, there will be no chance of clipping the low level peaks.

Another object is to prevent clashing of the two conductors.

This is accomplished by staggering the two conductors, one slightly above the other, so that, as in the case of an instantaneously recorded high level sound, one conductor will be able to pass beneath the other without clashing. The speech current carrying conductor is placed between the plane of the biasing conductor and the slit forming members to allow for sharper focusing. That is, it is necessary to sharply focus the light from the exciter lamp onto both the edge of the speech conductor and the edge of the slit forming members so as to impress upon the moving iilm a series of sound Wave representations with as sharp an edge as possible to define the opaque and transparent portions. Due to the fact that the focus of the objective lens is usually very critical it is important that the speech conductor be placed as near to the slit forming members as possible. The biasing conductor does not require such critical focusing since the 50 edge produced thereby is not used to represent the sound waves.

More particularly referring to the drawing, Fig.

1 is an enlarged fragmentary View of a section r Qf moving picture film having a variable area b5 sound track recorded thereon in accordance with my improved light valve.

Fig. 2 is a schematic View showing the circuit for operating the light valve.

Fig. 3 is a transverse sectional view taken along the lines 3--3 of Fig. 4 of an improved type of light valve for recording variable area sound track.

i Fig. 4 is a sectional View taken along the lineY 4--4 of Fig. 3.

Fig. 5 is an enlarged fragmentary view showing the light slit and its accompanying vibratory conductors.

Referring to Figs. 3 and 4, the valve generally indicated at I comprises a magnetic frame 2. The frame 2 is composed of a lower baseplate 3 and an upper magnetic frame having a hollow core 5 in a central portion thereof. The core 5 forms one of the poles and is provided with a magnetizing coil 6 which is supplied with current of as vconstant an intensity as possible. A pole piece 1 is secured to the ybase plate 3 as by Yscrews 1 and has an aperture 8 therein communicating with a second aperture 9 in a base plate 3, both of which are substantially in alignment with the hollow core 5. Slit forming members Iii and Ii are secured to the upper surfaces of the pole piece 1 by means of clamping pieces I2 and I3 thus leaving a slit, or aperture I1 between their adjacent edges. Screws I4 hold the clamping pieces I2 and |3 in position. End pieces I5 and IS (Figs. 4 and 5) are provided to deiine the end of the slit I1 formed by the two pieces I0 and I|. This slit I1 has a relatively small width in com.- parison'to its length, being in the order of .5 mil wide and about 140 mils long, although these dimensions may be varied to suit various conditions. AV pair of insulated bridges I8 and I9 is provided on either side of the pole piece 1 and carries'a pair of conductors 20 and 2|. Each of the bridges I8 and I9 is provided with a pair of adjusting jaws 22 and 23. These jaws are preferably of a spring material and are secured at their rear edgesto the bridges I8 and I9 by means of screws 24 andr25. The forward ends of the yjaws 22 and 23 are engaged by suitable adjusting screws 26 and 21. Adjustment of these screws 26 and 21 causes sidewise movement of the conductors 2|! and 2|. The ends of the conductors 20 and 2| are secured upon rotatable windlasses 28, 29, 35 and 3|. Each of the windlasses 28 to 3|, inclusive, is carried by insulated blocks 5,0 secured to the base plate 3 as by screws 5|. A slotted head'52 Von each oiV the windlasses allows for adjustment to regulate the tension of the conductors 29 and 2|. Conductors 53, 54, 55, and`56 provide electrical connection between the windlasses 28 to 3|, inclusive, and terminals 51, 58, 59, and 6B, respectively. At one end of each of the conductors 20 and 2|, an'insulated spring pressed arm 32 is provided, which is pivotally mounted at 6| and urged outward by a spring 62.

This is secured withinv a loop formed by each of the conductors 2|] and 2| to prevent undue tension from'being applied to either of the conductors.r Experience has indicated that an angle of about one degree is satisfactoryY to produce a full modulation of the light beam. From now on I shall term oneV of the conductors 2|) as the envelope following conductor. Whenv either low level or no sound is being recorded, the conductor 20 Vlies normally Vin a position sho-wn by the full linesin Fig. 5. `At high level modulation of the Yconductor 2|, the conductor 29 lies in a position shown by the dotted lines 33 S0 as. Q @lOW maX- mum excursions without interference of the speech current carrying conductor 2|.

Referring now to Fig. 2 which is a schematic diagram of the circuit employed for operating Y the light valve, a microphone 34 is provided to receiverthe sounds desired to be recorded upon the sensitized surface of a moving iilmV 35. Speech currents produced in the microphone34 are amplied by means of a suitable amplier 35 and are passed through transformer 31 from whence they are fed to the conductor 2l through lines 38 and 39. The modulated voice currents which are passed through the conductor 2| set up a magnetic iieldproduced by the pole pieces 5 and 1 and thus cause movement of the conductor 2| so as to uncover a greater or a lessV Light from the exciterV length of the slit I1. lamp (I9 is projected through a condenser lens li Yand is focused preferably upon the conductor 2| and the slit I1 from whence it is projectedonto the lm 35 by means of an objective lens 42,

which reduces the image of the slit aboutV half size. Y

I will now describe the means for moving the conductor 29 in accordance with the amplitude of the sounds being recorded. A biasing current of constant potential is fed by a battery 41 to theY terminals of the conductor 2i] by means of lines 45 and i6 to hold it in a position shown by the full lines 2D of Fig. 5, when no or little sound is being recorded. An amplifier 93. and rectifier 44' are shunted across the terminals of thetrans former 31 and current passing therethrough is conducted by the lines A5 and 46 to the conductor 2l) in a direction opposing the steady current passed by the battery 6|. When low level sounds are being recorded, only a small amount of rectied current is passed through the rectifier M but' Y Y when high level sounds Vare recorded, a corre`A spondingly greater amount of rectified current is passed through the conductorV 29 in opposition to the sound so as to allow the edge 63 of the blocking portion 54 (Fig. l) to closely follow the peaks of the wave forms 66 which represent the sound modulations. Y Y Y The biasing of the conductor 20 may also be obtained by applying the rectied'current from the rectifier MV, which varies Vinaccordance with the amplitude of the sounds being recorded, di-

In this case, the

rectly to the conductor '729. battery 41 would Vbe omitted and the normal position ofthe conductor 2G would be mechanically adjusted so that at low level modulation, it would take the position shown by the full lines 29' (Fig. 5) With the increase in-amplitude'of the sound being recorded, the corresponding increase inV rectified current would shift the center of modulation of the conductor 2i) to theY dot and dash lines 33. Y

. Referring now to Fig. 3, it will be notedV thatV the conductors 2|) and 2 I are staggered one Vabove the other so as to prevent clashing. This is especiallyradvantageous when recording of staccato tric or magnetic lag to be moved out of the Yway' soon enough to allow the conductor 2 Ito moveto its maximum position. Y

It should also be noted that the speech conductor 2l is in a position next to the members I0 and Il defining the slit I1 to allow the beam of light from the exciter lamp 40 (Fig. 2) tobe sharply focused at a point between the plane of the conductor 2| and the plane of the members I and l I. In practice, this will produce a sharp edge to both the shadow of the conductor 2l and the shadow of the slit forming members I0 and ll. In the case of a critically focused beam of light, the distance between the plane of the envelope following conductor 2U and the plane of the members i0 and Il may cause the edge of the shadow of the conductor 20 to be slightly hazy; or fuzzy. In other Words, the edge 63 of the blocking portion 64 on the soundtrack 65 (Fig. 1) may not be sharply defined but will be slightly fuzzy. Due to the fact that the portion 64 is used merely for blocking out the clear portions of the positive sound track and also due to the fact that the fuzziness, if any, will be very small, it will be seen that it will not affect the quality of the sound or the amount of ground noise.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent, is:

l. A sound recording system for variable area typev sound records comprising a rectangular aperture forming member, a vibratile electrical conductor cooperating therewith, means for vibrating said conductor in accordance with sound Waves, a second vibratile conductor cooperating with said aperture, and means for moving said second conductor in accordance with the envelope of said sound waves, each of said conductors individually cooperating with said aperture to form separate light traces.

2. A system for recording an anti-ground noise type of sound record comprising means forming a rectilinear slit member, a vibratile electrical conductor angularly disposed across said slit, means for moving said conductor in accordance with sound waves, a second vibratile conductor angularly disposed across said slit, and means for moving said second conductor in accordance with the envelope of said sound waves, each of said conductors individually cooperating with said slit to form separate light traces.

3. A sound recording system for anti-ground noise type of variable area records comprising an opaque member having a rectilinear slit therein, a pair of separate vibratile electrical conductors cooperating with said slit, one of said conductors being disposed in a plane between the plane of the other conductor and said opaque member, means for moving one of said conductors in accordance with sound waves being recorded, means for moving the other of said conductors in accordance with the envelope of said sound waves, and means for directing a beam of light through the opening formed by said slit and said conductor.

4. A system for recording an anti-ground noise type of variable area sound record comprising, a member having a rectilinear slit therein, a vibratile current carrying conductor disposed at an acute angle across said slit and adjacent thereto, means for vibrating said conductor in accordance with sound Waves, a second vibratile current carrying conductor disposed at an acute angle across said slit and in a plane above that of said first mentioned conductor, means for moving said second conductor in accordance with the envelope of said sound waves, and means for dlrecting a beam of light through the opening formed by said slit and said conductors.

5. A sound recording system comprising a source of light, means for supporting a light sensitive material, means for projecting light from said source on said material, means for generating electrical currents corresponding to sound waves, a light valve interposed between said light source and light sensitive material, means for impressing said electrical currents on said valve, said valve comprising a pair of vibratile conductors, one of which vibrates in accordance with the sound waves and the other of which vibrates in accordance with the envelope of said sound waves, a rectangular slit forming member cooperating with said conductors, said conductors being mounted at an angle across said slit, and means for adjusting each of said conductors individually with respect to said slit.

6. A system for recording sound waves which comprises a light source, photographic film, means for transmitting light from said source to said photographic lm, means for varying the amount of transmitted light comprising a member having an elongated slit therein, a pair of electrical conductors arranged in a magnetic field and adjacent the slit in said member to dene a light transmitting slot, means for supplying electrical currents to one of said conductors to effect a variation in the space relation between said conductor and said other conductor in accordance with the instantaneous values of saidvcurrents, and means for supplying electrical currents to the other of said conductors to effect a variation in its space relation with respect to the other of said conductors in accordance with the envelope of said electrical currents, said conductors and said slit member being disposed in oblique relation to each other.

'7. In combination, a light source, a photographic lm, means for varying the amount of transmitted light from said source to said film, said means comprising a member having a fixed, elongated aperture therein and a pair of movable elements suspended in a magnetic eld and disposed in oblique relation to the aperture in said member, means to supply modulated Aelectrical currents to said movable element to effect a movement of one of said conductors with respect to the other of said conductors in accordance with the instantaneous values of said currents and means to supply currents to the other of said movable elements to effect movement thereof with respect to the rst mentioned electrical element in accordance with the envelope of\saicl modulated electrical currents.

8. The method of producing a variable areavariable density sound track having noise reduction with a light valve having a pair of electrical conductors disposed in oblique relationship to a iixed rectangular slit comprising vibrating one of said conductors with modulated electrical currents and vibrating the other of said conductors in accordance with the envelope of said currents, said first conductor being adapted to vibrate over the entire rectangular aperture at high amplitude currents and over the mid portion of said rectangular slit for loW amplitude currents, while said second conductor uncovers said slit at high amplitude currents and covers said slit in proportion to the amplitude of the envelope currents.

BURTON F. MILLER. 

